METHOD OF PREPARING OXALIC ACID

Abstract

The present invention provides a method of preparing oxalic acid (H.sub.2C.sub.2O.sub.4), the method at least comprising the steps of: (a) providing a metal formate (HCO.sub.2M) containing stream, wherein the metal (M) of the metal formate (HCO.sub.2M) is a monovalent metal selected from the group consisting of Li, Na, K, Cs, Rb and a mixture thereof; (b) heating the metal formate (HCO.sub.2M) containing stream thereby obtaining a metal oxalate (M.sub.2C.sub.2O.sub.4) containing stream; (c) subjecting the metal oxalate (M.sub.2C.sub.2O.sub.4) containing stream to electrodialysis, thereby obtaining at least oxalic acid (M.sub.2C.sub.2O.sub.4) and a metal hydroxide (MOH).

Claims

1. A method of preparing oxalic acid (H.sub.2C.sub.2O.sub.4), the method at least comprising the steps of: (a) providing a metal formate (HCO.sub.2M) containing stream, wherein the metal (M) of the metal formate (HCO.sub.2M) is a monovalent metal selected from the group consisting of Li, Na, K, Cs, Rb and a mixture thereof; (b) heating the metal formate (HCO.sub.2M) containing stream thereby obtaining a metal oxalate (M.sub.2C.sub.2O.sub.4) containing stream; (c) subjecting the metal oxalate (M.sub.2C.sub.2O.sub.4) containing stream to electrodialysis, thereby obtaining at least oxalic acid (H.sub.2C.sub.2O.sub.4) and a metal hydroxide (MOH).

2. The method according to claim 1, wherein the metal (M) of the metal formate (HCO.sub.2M) is selected from the group consisting of K, Cs, Rb and a mixture thereof.

3. The method according to claim 1, wherein the metal formate (HCO.sub.2M) is potassium formate (HCO.sub.2K).

4. The method according to claim 1, wherein the metal formate (HCO.sub.2M) has been obtained from a metal bicarbonate (MHCO.sub.3).

5. The method according to claim 4, wherein the metal bicarbonate (MHCO.sub.3) has been obtained from CO.sub.2 and a metal hydroxide (MOH).

6. The method according to claim 5, wherein the metal hydroxide (MOH) obtained in step (c) is recycled for use in obtaining the metal bicarbonate (MHCO.sub.3).

7. The method according to claim 1, wherein the metal oxalate (M.sub.2C.sub.2O.sub.4) containing stream subjected in step (c) comprises at most 10.0 wt. % (based on dry matter) carbonate.

8. The method according to claim 1, wherein the oxalic acid (H.sub.2C.sub.2O.sub.4) obtained in step (c) is reacted with hydrogen (H.sub.2) to obtain ethylene glycol (HOCH.sub.2CH.sub.2OH).

9. A method of preparing ethylene glycol (HOCH.sub.2CH.sub.2OH) from CO.sub.2, the method at least comprising the steps of: (i) reacting CO.sub.2 and a metal hydroxide (MOH) thereby obtaining a metal bicarbonate (MHCO.sub.3), wherein the metal (M) of the metal hydroxide (MOH) is a monovalent metal selected from the group consisting of Li, Na, K, Cs, Rb and a mixture thereof; (ii) reacting the metal bicarbonate (MHCO.sub.3) obtained in step (i) with hydrogen (H.sub.2) thereby obtaining a metal formate (HCO.sub.2M); (iii) heating the metal formate thereby obtaining a metal oxalate (M.sub.2C.sub.2O.sub.4); (iv) subjecting the metal oxalate (M.sub.2C.sub.2O.sub.4) to electrodialysis, thereby obtaining at least oxalic acid (H.sub.2C.sub.2O.sub.4) and a metal hydroxide (MOH); (v) reacting the oxalic acid (H.sub.2C.sub.2O.sub.4) obtained in step (iv) with hydrogen (H.sub.2) to obtain ethylene glycol (HOCH.sub.2CH.sub.2OH).

10. The method according to claim 9, wherein at least part of the metal hydroxide (MOH) obtained in step (iv) is recycled for use in step (i).

Description

EXAMPLES

Example 1

[0029] This Example 1 illustrates in general terms how ethylene glycol (HOCH.sub.2CH.sub.2OH) can be prepared from CO.sub.2. A schematic overview of the preparation method of Example 1 is depicted in FIG. 1.

a. Preparation of Metal Bicarbonate (MHCO.sub.3)

[0030] CO.sub.2 and potassium hydroxide (KOH) are reacted, e.g. as described by R. V. Williamson and J. H. Mathews in Ind. Eng. Chem., 1924, 1157, thereby obtaining potassium bicarbonate (KHCOJ.

b. Preparation of Metal Formate (HCO.sub.2M)

[0031] The potassium bicarbonate (KHCO.sub.3) obtained is subsequently reacted with hydrogen (H.sub.2), e.g. as described by Ryo Tanaka, Makoto Yamashita and Kyoko Nozaki in J. Am. Chem. Soc., 2009, 131, 14168, thereby obtaining potassium formate (HCO.sub.2K).

c. Preparation of Metal Oxalate (M.sub.2C.sub.2O.sub.4)

[0032] The potassium formate (HCO.sub.2K) is heated, e.g. as described in DE 660473, thereby obtaining potassium oxalate (K.sub.2C.sub.2O.sub.4).

d. Preparation of Oxalic Acid (H.sub.2C.sub.2O.sub.4)

[0033] Subsequently, the potassium oxalate (K.sub.2C.sub.2O.sub.4) is subjected to electrodialysis, thereby obtaining at least oxalic acid (H.sub.2C.sub.2O.sub.4) and potassium hydroxide (KOH). The KOH can be recycled for use in the preparation of the potassium bicarbonate described above.

e. Preparation of Ethylene Glycol (HOCH.sub.2CH.sub.2OH; ‘MEG’)

[0034] The oxalic acid (H.sub.2C.sub.2O.sub.4) may then be reacted with hydrogen (H.sub.2) to obtain ethylene glycol (HOCH.sub.2CH.sub.2OH).

[0035] FIG. 2 schematically shows an alternative method according to the present invention for preparing ethylene glycol (HOCH.sub.2CH.sub.2OH), wherein the metal formate (i.c. HCO.sub.2K) can be obtained by reacting a metal hydroxide (i.c. KOH) with carbon monoxide (CO).

Example 2

[0036] Example 2 describes in further detail how oxalic acid (H.sub.2C.sub.2O.sub.4) and potassium hydroxide (KOH) can be obtained by subjecting potassium oxalate (K.sub.2C.sub.2O.sub.4) to electrodialysis.

[0037] An electrodialysis cell as depicted in FIG. 3 was used. Electrodialysis cells are commercially available and can be obtained from e.g. Astom Corporation (Tokyo, Japan) or Fumatech GmbH (Bietigheim-Bissingen, Germany). The electrodialysis cell (referred to with 1 in FIG. 3) contained an anode 2 and a cathode 3. Between the anode 2 and cathode 3 a bipolar membrane 4 (Fumatech FBP, commercially available from Fumatech GmbH) and four repeating membrane stacks 5 were placed, thereby creating anode compartment a, cathode compartment e and further compartments b-d. Each membrane stack 5 consisted of an anion-exchange membrane 6 (Mega AMH, commercially available from Mega A.S. (Prague, Czech Republic)), a cation-exchange membrane 7 (Mega CMH, commercially available from Mega A.S.), and a bipolar membrane 8 (Fumatech FBP). The effective membrane surface was 100 cm.sup.2.

[0038] Diluted sulphuric acid was used for the anode compartment a and a sodium hydroxide solution for the cathode compartment e; both the diluted sulphuric acid and the sodium hydroxide solution had a conductivity of 20 mS/cm.

[0039] A potassium oxalate containing stream (which was obtained by heating potassium formate according to DE 660473; containing 900 g potassium oxalate, 40 g potassium formate and 50 g potassium carbonate in 2.7 kg water) was fed into the compartments c (i.e. between the anion-exchange membrane 6 and the cation-exchange membrane 7 in the stacks 5) thereby generating an oxalic acid in compartment b and potassium hydroxide in compartment d. The fluids were circulated through the respective compartments at a flow of 20-50 l/h. The electrodialysis cell was operated at ambient temperature to 35° C. at a constant voltage of 20V.

[0040] The experiment was stopped when the current density dropped due to exhaustion of the feed; this started happening after about 6 hours, when the current dropped to below 5 mA/cm.sup.2. Then the various streams were analysed.

[0041] Table 1 lists the amounts of potassium, oxalate, formate and carbonate (in g/kg (based on dry matter)) in the various streams. Further, Table 2 lists the current in mA/cm.sup.2 at indicated times.

TABLE-US-00001 TABLE 1 Potassium Oxalate Formate Carbonate [g/kg] [g/kg] [g/kg] [g/kg] Feed 121.00 128.00 4.94 6.00 (compartment C) Feed, after dialysis 1.69 1.56 0.03 0.53 Oxalic acid stream 0.41 66.40 3.19 0.04 (compartment B) Hydroxide stream 69.00 0.67 0.06 0.44 (compartment D)

TABLE-US-00002 TABLE 2 Current [mA/cm.sup.2] Time [hour] Example 2 Example 3 Example 4 0 18 21 18 1 31 35 30 2 38 41 32 3 41 39 3 4 41 26 — 5 42 7 — 6 24 — — 7 8 — —

Examples 3 and 4

[0042] Example 2 was repeated with two different feed streams (and resulting product streams) with the composition as given in Table 3 (Example 3) and Table 4 (Example 4) to show that the present invention works under various conditions. Table 2 above lists current in mA/cm.sup.2 at indicated times.

TABLE-US-00003 TABLE 3 Potassium Oxalate Formate Carbonate [g/kg] [g/kg] [g/kg] [g/kg] Feed 60.5 64.00 2.47 3.00 (compartment C) Feed, after dialysis 0.28 0.54 0.10 0.004 Oxalic acid stream 0.56 54.20 2.34 0.04 (compartment B) Hydroxide stream 48.5 0.22 0.20 0.22 (compartment D)

TABLE-US-00004 TABLE 4 Potassium Oxalate Formate Carbonate [g/kg] [g/kg] [g/kg] [g/kg] Feed 30.30 32.00 1.25 1.50 (compartment C) Feed, after dialysis 0.02 0.06 0.00 0.04 Oxalic acid stream 0.22 30.00 1.31 0.04 (compartment B) Hydroxide stream 26.00 0.15 0.03 0.41 (compartment D)

DISCUSSION

[0043] As can be seen from the Examples, the present invention provides a method for preparing oxalic acid, without the co-production of gypsum or other waste materials to be disposed of and without the need of large amounts of sulphuric acid. Further, the present invention provides a method of preparing ethylene glycol on the basis of oxalic acid and even a method of preparing ethylene glycol starting from CO.sub.2.

[0044] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.